Angela Trego

Multidimensional strain field measurements using fiber optic grating sensors

Fiber optic grating sensors written into polarization preserving optical fiber may be used to monitor multidimensional strain fields in composite materials. This paper provides an overview of the characterization and test of multiaxis fiber grating sensors formed by writing 1300 and 1550 nm fiber gratings into polarization preserving optical fiber. A discussion of the usage of these multiaxis fiber grating sensors to measure two and three dimensional strain fields will be made. A brief review of practical applications of the technology to measure shear strain, transverse strain gradients as well as axial and traverse strain will be made with emphasis on aerospace and civil structure applications.

Health monitoring of an adhesive joint using a multiaxis fiber grating strain sensor system

The use of adhesive joints in aerospace structures is becoming increasingly important. From this, arises the problem of assessing joint integrity quickly, non- intrusively, accurately, and inexpensively. Current methods of assessing joint integrity, such as ultrasonics and x- rays, are time intensive and difficult to interpret. Blue Road Researchs solution to monitoring adhesive joint integrity quickly and accurately is to embed non-intrusive, multidimensional optical fiber grating strain sensors into or adjacent to the joints. Aluminum double lap adhesive joints were instrumented with the multi-axis grating strain sensors into or adjacent to the joints. Aluminum double lap adhesive joints were instrumented with the multi-axis senors and subjected to tension and fatigue test. Each specimen contained one sensor located either near the bond, embedded at the edge of the bond, or embedded towards the inner bond area. The joints with senors embedded into the adhesive showed minimal strength degradation. Basically, the multiaxis fiber grating strain sensors were found to provide information about transverse strain, axial strain, and transverse strain gradients that can provide important information throughout the adhesive joint. By changing the orientation of the sensor, shear strain and its effects can be clearly measured.

Progress on monitoring of adhesive joints using multiaxis fiber grating sensors

Previously, the results of embedding multi-axis fiber gratings into adhesively bonded joints were discussed. This paper presents more information on the testing of the adhesive joints and techniques employed to successfully embed a fiber grating sensor into such structures. These techniques include orienting the fiber, marking its orientation, and preparing it for embedment into the adhesive. Also discussed are strain relief methods for the egress of the fiber.

Transversely loaded fiber optic grating strain sensors for aerospace applications

Most fiber grating sensor technology that has been developed to support strain sensing involves the measurement of axial strain. Fiber grating sensors are however capable of monitoring transverse as well as axial strain. This paper reviews a series of applications of this technology that are of particular interest to aerospace applications.